SURFICIAL GEOLOGIC MAP OF THE NORMAL WEST 7.5 MINUTE QUADRANGLE, MCLEAN COUNTY, ILLINOIS

The Normal West Quadrangle is located in McLean County, Illinois. The boundaries of the Quadrangle span from 40⁰30’00” to 40⁰37’30” north latitude and 89⁰00’ to 89⁰07’30” west longitude. Quaternary sediment units, as much as 100m in thickness overlie Pennsylvanian bedrock strata. Using data from the McLean County Soils Survey, sediment parent materials were determined, and the translated into sediment units. Water well data on repository at the Illinois State Geological Survey supplemented the soils data. After the formation contacts were defined, a field check was conducted to amend contact placements, and cross sections were prepared using correlations from water well data. Quaternary units are underlain by Pennsylvanian strata that vary in lithology. The major Quaternary sediment units present in the Quadrangle include the Wedron Group, the Henry Formation, the Peoria Formation, and the Cahokia Alluvium. The Wedron Group consists of the Tiskilwa and Lemont Formations. These two formations are pink and grey diamicts that are interpreted as glacial tills. They form ground and recessional moraine deposits. The Tiskiwa Till is present south of the Bloomington Moraine, while the Lemont is present to its north. The Henry Formation consists of sand and gravel deposits that are interpreted as glacial river and outwash fan deposits. The Peoria Formation is made up of a fine grained, yellow silt-clay that covers the surface of most of the mapping area, and is interpreted as loess deposits. The Cahokia Alluvium consists of river deposits of sand, gravel, and silt, and is the youngest unit in the mapping area.